[Geoff Winnington-Ball (RIP)]

Sean, it was a good aircraft in Vietnam... and yet even then with well-known critical parameters regards autorotation vis-a-vis airspeed & altitude. Lose an engine at such and such an altitude and above or below such and such a speed, and the crew is TOAST. They glide like rocks.

The sophistication of more modern machines includes narrowing those gaps in the performance and reliability - or survivability - curve.